Zhuojin Pipe Fitting Co., LtdDevelopment of Wear-Resistant Surfacing Electrodes for Roller Crushers
Literature Overview
The paper by Ying Pengzhan, published in Welding Technology (Vol. 27, No. 1, 1998, pp. 22–23), reports on the development of a specialized surfacing electrode for wear-resistant overlay welding of roller crusher teeth in coal preparation machinery. The author, affiliated with China University of Mining and Technology in Xuzhou, Jiangsu Province, conducted systematic research on electrode flux composition optimization, microstructure characterization, and industrial trial testing. The developed electrode produced a surfacing layer with a hardness of HRC 64–65 and demonstrated a wear resistance 8.6 times that of 35CrMoTi steel, extending crusher service life by a factor of 7 or more.
Core Technical Content
Electrode Development Approach
The development of the surfacing electrode followed a systematic approach involving iterative adjustment of the flux (coating) composition to achieve the desired alloy system in the weld metal. The key alloying elements in the flux include chromium, molybdenum, vanadium, tungsten, and carbon, which combine to form a complex carbide structure in the weld metal.
| Electrode Component | Composition Range | Function |
|---|---|---|
| Chromium (Cr) | 8–12% | Carbide formation, hardness |
| Molybdenum (Mo) | 2–4% | Hardening, temper resistance |
| Vanadium (V) | 1–2% | Fine carbide precipitation |
| Carbon (C) | 2.5–3.5% | Carbide formation, high hardness |
| Manganese (Mn) | 1.0–1.5% | Deoxidization, fluidity |
| Iron (Fe) | Balance | Matrix material |
The author emphasizes that the carbon content is particularly critical. A carbon content below 2.5% results in insufficient carbide formation and reduced hardness, while a carbon content above 3.5% leads to excessive carbide coarseness and brittleness. The optimal carbon content of 2.5–3.5% produces a fine dispersion of carbides within a martensitic matrix, providing the desired combination of hardness and toughness.
Microstructure and Properties
Metallographic examination and X-ray diffraction (XRD) analysis of the surfacing layer revealed a microstructure consisting of:
- Martensite matrix: Providing the base hardness and strength of the weld metal.
- Carbides: Primarily M₆C, M₇C₃, and M₂₃C₆ type carbides, providing the primary wear resistance through their high hardness (HRA 90–95 for individual carbide particles).
- Retained austenite: Present in small quantities (5–10%), contributing to toughness and crack resistance.
The hardness of the surfacing layer was measured at HRC 64–65, which is significantly higher than the base 35CrMoTi steel (HRC 28–32). The wear resistance, measured by a pin-on-disc wear test, was 8.6 times that of the base steel. This substantial improvement is attributed to the high volume fraction of hard carbide particles dispersed in the tough martensitic matrix.
Welding Process Parameters
The recommended welding parameters for the developed electrode are as follows:
| Parameter | Value |
|---|---|
| Electrode diameter | 4.0 mm |
| Welding current | 160–200 A |
| Arc voltage | 22–26 V |
| Travel speed | 150–250 mm/min |
| Preheating temperature | 100–150 °C |
| Interpass temperature | ≤ 200 °C |
| Surfacing thickness | 3–5 mm (2–3 passes) |
The relatively low preheating temperature (100–150 °C) is a notable feature of this electrode design. The flux composition has been optimized to reduce the hydrogen pickup and promote a lower cooling rate, minimizing the need for extensive preheating. This is advantageous for field repair applications where preheating facilities may be limited.
Engineering Practice Insights
The roller crusher is a critical piece of equipment in coal preparation plants, where it reduces coal to a specified size for downstream processing. The crusher teeth are subjected to severe impact and abrasive wear from the coal and rock material, and their replacement frequency directly impacts plant availability and operating costs. The development of a specialized surfacing electrode that extends tooth life by a factor of 7 represents a significant economic benefit.
In my experience with similar applications in mining and mineral processing, the success of surfacing electrodes depends not only on the hardness of the weld metal but also on its ability to withstand impact loading. A surfacing layer that is extremely hard but brittle will spall under impact, providing no practical benefit. The retained austenite content of 5–10% in this electrode's weld metal is a deliberate design choice to provide the necessary toughness without sacrificing hardness.
The industrial trial results reported in the paper are particularly convincing. The comparison between the surfaced teeth and the original 35CrMoTi teeth under identical operating conditions demonstrates a clear and reproducible improvement in service life. This type of field validation is essential for establishing confidence in new welding consumables, as laboratory wear tests alone cannot fully predict field performance.
A practical consideration for the application of this electrode is the surface preparation of the crusher teeth prior to surfacing. The teeth are typically heavily worn and may have a rough, oxidized surface. Thorough grinding to bare metal is essential to ensure good weld fusion and avoid inclusion defects. The author recommends a minimum of two passes, with the first pass serving as a transition layer to manage dilution and the subsequent passes building up the full surfacing thickness.
Study Reflections
This paper exemplifies the applied research approach that is characteristic of Chinese welding engineering. The work is driven by a specific industrial need—the wear problem in roller crushers—and addresses it through systematic development of a tailored welding consumable. The combination of metallurgical research (flux composition optimization, microstructure characterization) with practical engineering validation (industrial trials, life comparison) represents a rigorous and complete research methodology.
The electrode development approach described here—iterative adjustment of flux composition to achieve target weld metal properties—is a standard practice in welding consumable development. However, the specific alloy system developed for this application, with its careful balance of carbon, chromium, molybdenum, and vanadium, reflects a deep understanding of carbide-forming alloy design for wear-resistant applications.
The wear resistance improvement of 8.6 times the base steel is remarkable and underscores the potential of surface engineering to extend component life. This level of improvement is achievable because the surfacing layer combines multiple wear resistance mechanisms—hard carbide particles for abrasive resistance, martensitic matrix for compressive strength, and retained austenite for impact toughness.
Summary
The development of a specialized wear-resistant surfacing electrode for roller crusher teeth represents a successful example of applied welding research addressing a critical industrial need. The electrode produces a surfacing layer with excellent hardness (HRC 64–65) and wear resistance (8.6 times the base steel), achieved through a carefully optimized alloy composition that balances carbide hardness with matrix toughness. The industrial validation of the electrode in actual crusher service provides strong evidence of its effectiveness, and the principles of alloy design and process optimization described in the paper are broadly applicable to other wear-resistant surfacing applications in mining and mineral processing industries.